- 2079 Baisakh · 3 marks
Control memory vs main memory
Short answer
Control memory holds microprograms, is ROM, very fast, small, inside the CPU, and invisible to the programmer. Main memory stores user programs and data, is RAM, larger, slower, external on the system bus, and programmer-visible.
Differentiate between control memory and main memory.
| Basis | Control memory | Main memory |
|---|---|---|
| Contents | Microprograms (microinstructions) | User programs and data |
| Type | ROM (read only; sometimes writable control store) | RAM (read and write) |
| Location | Inside the control unit of the CPU | Outside the CPU, on the system bus |
| Used by | Control unit, to produce control signals | CPU, I/O and the programmer |
| Speed | Very fast | Slower |
| Size | Small (for example 128 to a few K words) | Large (MB to GB) |
| Word width | Wide (microinstruction, e.g. 20 bits or more) | Equals word length of the machine |
| Visible to programmer | No | Yes |
| Addressed by | Control address register (CAR) | Address register (AR / MAR) |
✓ Answer checked by Claude Opus 5.5 (high effort)
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